When formulating new catalysts, a large number of candidate catalyst compositions may be synthesized. It then becomes important to evaluate each of the candidate catalysts to determine the formulations that are the most successful in catalyzing the reaction of interest under a given set of reaction conditions. Two key characteristics of a catalyst that are determinative of its success are the activity of that catalyst and the selectivity of the catalyst. The term “activity” refers to the rate of conversion of reactants by a given amount of catalyst under specified conditions, and the term “selectivity” refers to the degree to which a given catalyst favors one reaction compared with another possible reaction; see McGraw-Hill Concise Encyclopedia of Science and Technology, Parker, S. B., Ed. in Chief; McGraw-Hill: New York, 1984; p. 854. From the activity and selectivity values, yields may be calculated, and it is advantageous to compare various catalysts based on the activity, selectivity and yields achieved.
The traditional approach to evaluating the activity, selectivity, and yield of new catalysts is a sequential one. In a microreactor or pilot plant, each catalyst is independently serially tested at one or more sets of specified conditions. In most cases, the microreactor or pilot plant is operated in a fixed bed mode. Occasionally, when the ultimate end use of the catalyst is envisioned as being in a fluidized bed application, the catalysts may be tested using a pilot plant operated in a fluidized bed mode. Upon completion of the tests at one or more sets of conditions, the current catalyst is removed from the microreactor or pilot plant and the next catalyst is loaded. The testing is repeated on the freshly loaded catalyst. The process is repeated sequentially for each of the catalyst formulations. Overall, the process of testing all new catalyst formulations is a lengthy process at best.
Developments in combinatorial chemistry have first largely concentrated on the synthesis of chemical compounds. For example, U.S. Pat. Nos. 5,612,002 and 5,766,556 disclose a method and apparatus for multiple simultaneous synthesis of compounds. WO 97/30784-A1 discloses a microreactor for the synthesis of chemical compounds. Akporiaye, D. E.; Dahl, I. M.; Karlsson, A.; Wendelbo, R. Angew Chem. Int. Ed. 1998, 37, 609-611 disclose a combinatorial approach to the hydrothermal synthesis of zeolites, see also WO 98/36826. Other examples include U.S. Pat. Nos. 5,609,826, 5,792,431, 5,746,982, and 5,785,927, and WO 96/11878-A1.
More recently, combinatorial approaches have been applied to catalyst testing to try to expedite the testing process. For example, WO 97/32208-A1 teaches placing different catalysts in a multicell holder. The reaction occurring in each cell of the holder is measured to determine the activity of the catalysts by observing the heat liberated or absorbed by the respective formulation during the course of the reaction and/or analyzing the products or reactants. Thermal imaging had been used as part of other combinatorial approaches to catalyst testing, see Holzwarth, A.; Schmidt, H.; Maier, W. F. Angew. Chem. Int. Ed., 1998, 37, 2644-2647, and Bein, T. Angew. Chem. Int. Ed., 1999, 38, 323-326. Thermal imaging may be a tool to learn some semi-quantitative information regarding the activity of the catalyst, but it provides no indication as to the selectivity of the catalyst.
Some attempts to acquire information as to the reaction products in rapid-throughput catalyst testing are described in Senkam, S. M. Nature, July 1998, 384(23), 350-353, where laser-induced resonance-enhanced multiphoton ionization is used to analyze a gas flow from each of the fixed catalyst sites. Similarly, Cong, P.; Doolen, R. D.; Fan, Q.; Giaquinta, D. M.; Guan, S.; McFarland, E. W.; Poojary, D. M.; Self, K.; Turner, H. W.; Weinberg, W. H. Angew Chem. Int. Ed. 1999, 38, 484-488 teaches using a probe with concentric tubing for gas delivery/removal and sampling. Only the fixed bed of catalyst being tested is exposed to the reactant stream, with the excess reactants being removed via vacuum. The single fixed bed of catalyst being tested is heated and the gas mixture directly above the catalyst is sampled and sent to a mass spectrometer.
Combinatorial chemistry has been applied to evaluate the activity of catalysts. Some applications have focused on determining the relative activity of catalysts in a library; see Klien, J.; Lehmann, C. W.; Schmidt, H.; Maier, W. F. Angew Chem. Int. Ed. 1998, 37, 3369-3372; Taylor, S. J.; Morken, J. P. Science, April 1998, 280(10), 267-270; and WO 99/34206-A1. Some applications have broadened the information sought to include the selectivity of catalysts. WO 99/19724-A1 discloses screening for activities and selectivities of catalyst libraries having addressable test sites by contacting potential catalysts at the test sites with reactant streams forming product plumes. The product plumes are screened by passing a radiation beam of an energy level to promote photoions and photoelectrons which are detected by microelectrode collection. WO 98/07026-A1 discloses miniaturized reactors where the reaction mixture is analyzed during the reaction time using spectroscopic analysis. Some commercial processes have operated using multiple parallel reactors where the products of all the reactors are combined into a single product stream; see U.S. Pat. Nos. 5,304,354 and 5,489,726.
Applicants have developed a process to simultaneously test a plurality of catalysts in a rapid, economical, accurate, and consistent way. Applicants' invention fluidizes the multiple catalyst beds in an array of reactors so that the temperature of each catalyst bed can be accurately set, measured, and/or controlled, thereby providing for valid comparisons of catalyst performance among multiple catalysts. Applicants' invention calls for fluidization of the multiple of catalyst beds independent of whether the ultimate application of the catalyst is in a fixed bed process or in a fluidized bed process.